in the rough center

Senior Member

Now she pinched it between her thumb and finger and tried to draw it from the earth like a loose tooth from a gum. It didn’t come. She was gripping the protrusion in the rough center. It sank back into the earth –or that was the impression she had then –on either side at a width of less than two inches.

Source: The Tommyknockers by Stephen King

Does in the rough centre = roughly in the centre? Is rough in the bolded expression an adverb or an adjective?
Thank you